Tracked vehicles are well known. They are generally used where the terrain is rough and unpredictable. Tracked vehicles are useful under user control, as well as for partially and fully autonomous mobile robots. One of the challenges with mobile robots is to provide a robot that can ascend and descend stairs, slopes, cross ditches, surmount certain obstacles, and generally operate over rough terrain whether moving forward or backward, turning on spot, etc.
One such mobile robot was suggested in U.S. Pat. No. 4,483,407 which shows an articulated track vehicle. This mobile robot includes an auxiliary arm supporting a planetary wheel on both sides of the platform. The arms could operate on either side of the track: between the main body and the track, or on the other side of the track on the exterior of the mobile robot perimeter defined by the tracks. Each auxiliary arm is connected to the mobile robot platform with first and second arm linkages. The first arm is pivotally attached to the platform, the second arm is pivotally attached to the distal end of the first arm, and the planetary wheel is attached to the distal end of the second arm. The auxiliary arm is controlled such that the planetary wheel is exerting a tension onto the track. This auxiliary arm is pivoting in a plane parallel to the track longitudinal plane defined as cutting through the two sides of the belt: the upper and lower and perpendicular to the belt width. The arm plane depending on arm location is either located between the platform and track, or on the outside of the track. In the former the arm is actuated using a spring-slide-bar mechanism, and in the latter the arm is actuated using a gear-sprocket-mechanism. This vehicle has a number of disadvantages. Specifically, in the implementation using a spring-slide-bar mechanism it is impossible to ensure continuous tensioning of the track during the motion of the auxiliary wheel. This is the result of the arm mechanism design, which can not ensure an optimal path (perfect ellipse) of the planetary wheel. In addition, the location of the arm does not allow a full rotation of the arm because of interference with the platform pulleys axles. This reduces the effectiveness of the articulated track whose main purpose is to support motion on rough terrain, stairs, etc. In the implementation using a gear-sprocket mechanism there are no springs, therefore continuous tensioning of the track is impossible as the track may undergo variations in length due to operating conditions or stresses in directions that are not compensated actively by the track and arm mechanisms. Furthermore, this transmission mechanism is complicated as it involves six gears, 2 sprockets, and 1 chain, thus raising the cost of manufacturing and lowering the reliability.
Another such robot is INUKTUN VGTV. This mobile robot is small and light. It has an articulated track mechanism. The mechanism has an arm and a planetary wheel, both attached to the chassis on each side. It has a camera mounted on a platform attached to a common member connecting the two planetary wheels. The articulated tracks are used to raise the camera for surveillance and inspection. The articulated track mechanism has six moving members activated by one motor. This vehicle has a number of disadvantages. Specifically, it has limited variation of the track configuration in one direction only. It has very limited capability to operate on rough terrain. It cannot climb stairs because it is impossible to ensure tensioning of the track based on the articulated track mechanism. The mechanism does not ensure an optimal trajectory (perfect ellipse) of the planetary wheel, as there is no fixed focus of the ellipse. Further, the six-member planetary wheel mechanism is costly to manufacture and install.
Another such robot is shown in U.S. Pat. No. 6,668,951 which discloses a robot which includes a main section and a forward section. The forward section includes an elongate arm (flipper) that is pivotally attached to the front of the main section. The elongate arm has a length that is shorter than half of the main section. This vehicle has some disadvantages. Specifically the location of the centre of gravity cannot be changed adequately during the execution of a task to ensure the stability of the robot. The control of the location of center of gravity is very limited, with potential consequences such as instability on ascent or descent of steep (45 deg) stairs. Also, the vehicle can effectively move over obstacles only with the front end where the elongate arm is connected. Further, this vehicle's capability to cross wider ditches is somewhat limited relative to the platform length.
Accordingly it would be advantageous to provide a tracked vehicle that can overcome all of the disadvantages of the prior art as mentioned above, which are: (i) non-continuous tensioning of the track; and (ii) narrow variation of the location of the center of mass. The mobile robot would be adaptable to different terrains and would be suitable for traveling over a variety of surfaces and obstacles, including stairways and ditches. It would move in either direction with similar capability. It would flip over and perform as well in either orientation. Further it would be advantageous to provide a user-controlled active terrain adaptability of the vehicle with a variable (articulated) track configuration that can be regulated to suit real-time surface conditions. Also, it would be advantageous to make possible scaling up and down the basic design for smaller and larger mobile robots thus increasing the capability to perform a wider variety of tasks. Also, it would be advantageous to provide a vehicle that could withstand impact due to free fall from a height of approximately 2 m. Still further it would be advantageous to provide such a vehicle in a cost effective manner.